Auto merge of #2623 - alexcrichton:nfs-lol-no, r=brson
Auto merge of #2623 - alexcrichton:nfs-lol-no, r=brson

Don't use flock on NFS mounts

Completely skip file locking when we detect an NFS mount via `statfs`.

Closes #2615

vojtechkral/cargo,rust-lang/cargo,tshepang/cargo,brson/cargo,tshepang/cargo,blaenk/cargo,tsurai/cargo,AndiDog/cargo,mark-buer/cargo,rust-lang/cargo,tshepang/cargo,achanda/cargo,durka/cargo,tsurai/cargo,tsurai/cargo,durka/cargo,mark-buer/cargo,rustyhorde/cargo,tshepang/cargo,mark-buer/cargo,sbeckeriv/cargo,sbeckeriv/cargo,eminence/cargo,rustyhorde/cargo,brson/cargo,vojtechkral/cargo,achanda/cargo,eminence/cargo,nipunn1313/cargo,sbeckeriv/cargo,nipunn1313/cargo,AndiDog/cargo,nipunn1313/cargo,nipunn1313/cargo,vojtechkral/cargo,mark-buer/cargo,brson/cargo,eminence/cargo,blaenk/cargo,rustyhorde/cargo,vojtechkral/cargo,rust-lang/cargo,mark-buer/cargo,eminence/cargo,rust-lang/cargo,AndiDog/cargo,durka/cargo,brson/cargo,durka/cargo,tsurai/cargo,achanda/cargo,achanda/cargo,brson/cargo,rustyhorde/cargo,sbeckeriv/cargo,blaenk/cargo,AndiDog/cargo,blaenk/cargo,blaenk/cargo,AndiDog/cargo,tsurai/cargo